[RFC] arm: add relocate initrd support

[yalin wang]

> On Oct 10, 2015, at 00:10, Russell King - ARM Linux <linux at arm.linux.org.uk> wrote:
> 
> On Fri, Oct 09, 2015 at 11:55:09PM +0800, yalin wang wrote:
>> Add support for initrd on ARM arch, in case
>> mem= boot option change the memory size or the initrd are
>> not placed in low memory region, we need copy the initrd
>> to low memory region.
>> 
>> Signed-off-by: yalin wang <yalin.wang2010 at gmail.com>
>> ---
>> arch/arm/include/asm/fixmap.h |  1 +
>> arch/arm/kernel/setup.c       | 72 +++++++++++++++++++++++++++++++++++++++++++
>> 2 files changed, 73 insertions(+)
>> 
>> diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
>> index 58cfe9f..18ad90f 100644
>> --- a/arch/arm/include/asm/fixmap.h
>> +++ b/arch/arm/include/asm/fixmap.h
>> @@ -10,6 +10,7 @@
>> 
>> enum fixed_addresses {
>> 	FIX_EARLYCON_MEM_BASE,
>> +	FIX_RELOCATE_INITRD,
>> 	__end_of_permanent_fixed_addresses,
>> 
>> 	FIX_KMAP_BEGIN = __end_of_permanent_fixed_addresses,
>> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
>> index 20edd34..4260d59 100644
>> --- a/arch/arm/kernel/setup.c
>> +++ b/arch/arm/kernel/setup.c
>> @@ -811,6 +811,77 @@ static void __init request_standard_resources(const struct machine_desc *mdesc)
>> 		request_resource(&ioport_resource, &lp2);
>> }
>> 
>> +#if defined(CONFIG_BLK_DEV_INITRD) && defined(CONFIG_MMU)
>> +/*
>> + * Relocate initrd if it is not completely within the linear mapping.
>> + * This would be the case if mem= cuts out all or part of it
>> + * or the initrd are not in low mem region place.
>> + */
>> +static void __init relocate_initrd(void)
>> +{
>> +	phys_addr_t orig_start = __virt_to_phys(initrd_start);
>> +	phys_addr_t orig_end = __virt_to_phys(initrd_end);
> 
> If initrd_start or initrd_end are outside of the lowmem region, it's
> quite possible for these to return incorrect physical addresses.
> The generic kernel's idea of using virtual addresses for the initrd
> stuff is painfully wrong IMHO.
> 
> The unfortunate thing is that the DT code propagates this stuff:
> 
>        initrd_start = (unsigned long)__va(start);
>        initrd_end = (unsigned long)__va(end);
> 
> and even this can give wrong results for the virtual address when the
> physical is outside of lowmem.  For addresses outside of lowmem,
> __virt_to_phys(__va(start)) is not guaranteed to return 'start'.
> 
> This is why I've said that if we want to support ramdisks outside of
> the lowmem mapping, we need to get rid of the initrd_start/initrd_end
> virtual addresses.
> 
> I'm sorry, but we need much wider code changes before we can cope with
> this.
> 
>> +	phys_addr_t ram_end = memblock_end_of_DRAM();
>> +	phys_addr_t new_start;
>> +	phys_addr_t src;
>> +	unsigned long size, to_free = 0;
>> +	unsigned long slop, clen, p;
>> +	void *dest;
>> +
>> +	if (orig_end <= memblock_get_current_limit())
>> +		return;
>> +
>> +	/*
>> +	 * Any of the original initrd which overlaps the linear map should
>> +	 * be freed after relocating.
> 
> How does this work?  The code in arm_memblock_init() will have already
> reserved the physical addresses for the ramdisk:
> 
> 	memblock_reserve(phys_initrd_start, phys_initrd_size);
> 
> So any new allocation shouldn't overlap the existing ramdisk - unless
> this is wrong.
>  
i see, i will send a V2 patch for review .

Thanks